System and method of broad band optical end point detection for film change indication

ABSTRACT

A system and method for detecting an endpoint is disclosed that includes illuminating a first portion of a surface of a wafer with a first broad beam of light. A first reflected spectrum data is received. The first reflected spectrum of data corresponds to a first spectra of light reflected from the first illuminated portion of the surface of the wafer. A second portion of the surface of the wafer with a second broad beam of light. A second reflected spectrum data is received. The second reflected spectrum of data corresponds to a second spectra of light reflected from the second illuminated portion of the surface of the wafer. The first reflected spectrum data is normalized and the second reflected spectrum data is normalized. An endpoint is determined based on a difference between the normalized first spectrum data and the normalized second spectrum data.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of and claims priorityfrom U.S. patent application Ser. No. 10/112,425 filed on Mar. 29, 2002and entitled “System and Method of Broad Band Optical End PointDetection for Film Change Indication,” which is incorporated herein byreference in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates generally to endpoint detection in achemical mechanical polishing process, and more particularly to endpointdetection using optical interference of a broad reflectance spectrum.

[0004] 2. Description of the Related Art

[0005] In the fabrication of semiconductor devices, typically, theintegrated circuit devices are in the form of multi-level structures. Atthe substrate level, transistor devices having diffusion regions areformed. In subsequent levels, interconnect metallization lines arepatterned and electrically connected to the transistor devices to definethe desired functional device. As is well known, patterned conductivelayers are insulated from other conductive layers by dielectricmaterials, such as silicon dioxide. As more metallization levels andassociated dielectric layers are formed, the need to planarize thedielectric material increases. Without planarization, fabrication ofadditional metallization layers becomes substantially more difficult dueto the higher variations in the surface topography. In otherapplications, metallization line patterns are formed in the dielectricmaterial, and then metal chemical mechanical polishing (CMP) operationsare performed to remove excess metallization.

[0006] In the prior art, CMP systems typically implement belt, orbital,or brush stations in which belts, pads, or brushes are used to scrub,buff, and polish one or both sides of a wafer. Slurry is used tofacilitate and enhance the CMP operation. Slurry is most usuallyintroduced onto a moving preparation surface, e.g., belt, pad, brush,and the like, and distributed over the preparation surface as well asthe surface of the semiconductor wafer being buffed, polished, orotherwise prepared by the CMP process. The distribution is generallyaccomplished by a combination of the movement of the preparationsurface, the movement of the semiconductor wafer and the frictioncreated between the semiconductor wafer and the preparation surface.

[0007]FIG. 1A shows a cross sectional view of a dielectric layer 102undergoing a fabrication process that is common in constructingdamascene and dual damascene interconnect metallization lines. Thedielectric layer 102 has a diffusion barrier layer 104 deposited overthe etch-patterned surface of the dielectric layer 102. The diffusionbarrier layer, as is well known, is typically titanium nitride (TiN),tantalum (Ta), tantalum nitride (TaN) or a combination of tantalumnitride (TaN) and tantalum (Ta). Once the diffusion barrier layer 104has been deposited to the desired thickness, a copper layer 106 isformed over the diffusion barrier layer in a way that fills the etchedfeatures in the dielectric layer 102. Some excessive diffusion barrierand metallization material is also inevitably deposited over the fieldareas. In order to remove these overburden materials and to define thedesired interconnect metallization lines and associated vias (notshown), a chemical mechanical planarization (CMP) operation isperformed.

[0008] As mentioned above, the CMP operation is designed to remove thetop metallization material from over the dielectric layer 102. Forinstance, as shown in FIG. 1B, the overburden portion of the copperlayer 106 and the diffusion barrier layer 104 have been removed. As iscommon in CMP operations, the CMP operation must continue until all ofthe overburden metallization and diffusion barrier material 104 isremoved from over the dielectric layer 102. However, in order to ensurethat all the diffusion barrier layer 104 is removed from over thedielectric layer 102, there needs to be a way of monitoring the processstate and the state of the wafer surface during its CUT processing. Thisis commonly referred to as endpoint detection. Endpoint detection forcopper is performed because copper cannot be successfully polished usinga timed method. A timed polish does not work with copper because theremoval rate from a CMP process is not stable enough for a timed polishof a copper layer. The removal rate for copper from a CMP process variesgreatly. Hence, monitoring is needed to determine when the endpoint hasbeen reached. In multi-step CMP operations there is a need to ascertainmultiple endpoints: (1) to ensure that Cu is removed from over thediffusion barrier layer; (2) to ensure that the diffusion barrier layeris removed from over the dielectric layer. Thus, endpoint detectiontechniques are used to ensure that all of the desired overburdenmaterial is removed.

[0009] Many approaches have been proposed for the endpoint detection inCMP of metal. The prior art methods generally can be classified asdirect and indirect detection of the physical state of polish. Directmethods use an explicit external signal source or chemical agent toprobe the wafer state during the polish. The indirect methods on theother hand monitor the signal internally generated within the tool dueto physical or chemical changes that occur naturally during thepolishing process.

[0010] Indirect endpoint detection methods include monitoring: thetemperature of the polishing pad/wafer surface, vibration of polishingtool, frictional forces between the pad and the polishing head,electrochemical potential of the slurry, and acoustic emission.Temperature methods exploit the exothermic process reaction as thepolishing slurry reacts selectively with the metal film being polished.U.S. Pat. No. 5,643,050 is an example of this approach. U.S. Pat. No.5,643,050 and U.S. Pat. No. 5,308,438 disclose friction-based methods inwhich motor current changes are monitored as different metal layers arepolished.

[0011] Another endpoint detection method disclosed in Europeanapplication EP 0 739 687 A2 demodulates the acoustic emission resultingfrom the grinding process to yield information on the polishing process.Acoustic emission monitoring is generally used to detect the metalendpoint. The method monitors the grinding action that takes placeduring polishing. A microphone is positioned at a predetermined distancefrom the wafer to sense acoustical waves generated when the depth ofmaterial removal reaches a certain determinable distance from theinterface to thereby generate output detection signals. All thesemethods provide a global measure of the polish state and have a strongdependence on process parameter settings and the selection ofconsumables. However, none of the methods except for the frictionsensing have achieved some commercial success in the industry.

[0012] Direct endpoint detection methods monitor the wafer surface usingacoustic wave velocity, optical reflectance and interference,impedance/conductance, electrochemical potential change due to theintroduction of specific chemical agents. U.S. Pat. No. 5,399,234 andU.S. Pat. No. 5,271,274 disclose methods of endpoint detection for metalusing acoustic waves. These patents describe an approach to monitor theacoustic wave velocity propagated through the wafer/slurry to detect themetal endpoint. When there is a transition from one metal layer intoanother, the acoustic wave velocity changes and this has been used forthe detection of endpoint. Further, U.S. Pat. No. 6,186,865 discloses amethod of endpoint detection using a sensor to monitor fluid pressurefrom a fluid bearing located under the polishing pad. The sensor is usedto detect a change in the fluid pressure during polishing, whichcorresponds to a change in the shear force when polishing transitionsfrom one material layer to the next. Unfortunately, this method is notrobust to process changes. Further, the endpoint detected is global, andthus the method cannot detect a local endpoint at a specific point onthe wafer surface. Moreover, the method of the U.S. Pat. No. 6,186,865patent is restricted to a linear polisher, which requires an airbearing.

[0013] There have been many proposals to detect the endpoint using theoptical reflectance from the wafer surface. They can be grouped into twocategories: monitoring the reflected optical signal at a singlewavelength using a laser source or using a broad band light sourcecovering the full visible range of the electromagnetic spectrum. U.S.Pat. No. 5,433,651 discloses an endpoint detection method using a singlewavelength in which an optical signal from a laser source is impinged onthe wafer surface and the reflected signal is monitored for endpointdetection. The change in the reflectivity as the polish transfers fromone metal to another is used to detect the transition.

[0014] Broad band methods typically rely on using information inmultiple wavelengths of the electromagnetic spectrum. U.S. Pat. No.6,106,662 discloses using a spectrometer to acquire an intensityspectrum of reflected light in the visible range of the opticalspectrum. Two bands of wavelengths are selected in the spectra thatprovide good sensitivity to reflectivity change as polish transfers fromone metal to another. A detection signal is then defined by computingthe ratio of the average intensity in the two bands selected.Significant shifts in the detection signal indicate the transition fromone metal to another.

[0015] A common problem with current endpoint detection techniques isthat some degree of over-polishing is required to ensure that all of theconductive material (e.g., metallization material or diffusion barrierlayer 104) is removed from over the dielectric layer 102 to preventinadvertent electrical interconnection between metallization lines. Aside effect of improper endpoint detection or over-polishing is thatdishing 108 occurs over the metallization layer that is desired toremain within the dielectric layer 102. The dishing effect essentiallyremoves more metallization material than desired and leaves a dish-likefeature over the metallization lines. Dishing is known to impact theperformance of the interconnect metallization lines in a negative way,and too much dishing can cause a desired integrated circuit to fail forits intended purpose.

[0016] Prior art methods typically can only approximately predict theactual end point but cannot actually detect the actual end point. Theprior art detects when the intensity of a few wavelengths change, suchas occurs when a material becomes translucent (e.g., the materialbecomes substantially transparent to some wavelengths but not allwavelengths). When the material becomes translucent, the intensities ofsome wavelengths change because those wavelengths are being reflected bythe layer below the material currently being removed.

[0017] Because the event actually detected by the prior art process iswhen the layer being removed (such as a metal layer) becomes translucentrather than nonexistent (i.e., fully removed), the prior art processmust then predict an actual end point (i.e., when all of the desiredmaterial is actually fully removed). In one example, the actual eventdetected, the translucent point, occurs when the material is 500 Åthick. From previous processes, the CMP process is known to be removingmaterial at a rate of 3000 Å per minute. Therefore, the actual end pointis predicted by the Formula 1 below:

(translucent material thickness)/(material removal rate)=time delay topredicted end point  Formula 1:

[0018] In current example: (500 Å)/(3000 Å/minute)=10 seconds

[0019] Therefore, the prior art CMP process then continues the CMPremoval process for an additional 10 seconds after the actual detectionevent occurs. Further, this time delay is calculated based on priorexperience and also assumes a constant removal rate.

[0020] In view of the foregoing, there is a need for endpoint detectionsystems and methods that improve accuracy in endpoint detection.

SUMMARY OF THE INVENTION

[0021] Broadly speaking, the present invention fills these needs byproviding a system and method of broad band optical end point detection.It should be appreciated that the present invention can be implementedin numerous ways, including as a process, an apparatus, a system,computer readable media, or a device. Several inventive embodiments ofthe present invention are described below.

[0022] A method for detecting an endpoint is disclosed that includesilluminating a first portion of a surface of a wafer with a first broadbeam of light. A first reflected spectrum data is received. The firstreflected spectrum of data corresponds to a first spectra of lightreflected from the first illuminated portion of the surface of thewafer. A second portion of the surface of the wafer is illuminated witha second broad beam of light. A second reflected spectrum data isreceived. The second reflected spectrum of data corresponds to a secondspectra of light reflected from the second illuminated portion of thesurface of the wafer. The first reflected spectrum data is normalizedand the second reflected spectrum data is normalized. An endpoint isdetermined based on a difference between the normalized first spectrumdata and the normalized second spectrum data.

[0023] In one embodiment, the first spectrum data includes an intensitylevel corresponding to each of the wavelengths in the correspondingfirst spectra. In one embodiment, the second spectrum data includes anintensity level corresponding to each of the wavelengths in thecorresponding second spectra.

[0024] In one embodiment, the wavelengths in the first spectra and thesecond spectra can include a range of about 300 nm to about 720 nm. Inone embodiment the first spectra and the second spectra can include arange of about 200 to about 520 individual data points.

[0025] In one embodiment, normalizing the first spectrum data includessubstantially removing the process related intensity fluctuations whichare removed by substantially removing the corresponding intensityvalues. In one embodiment, normalizing the second spectrum data includessubstantially removing the process related intensity fluctuations whichare removed by substantially removing the corresponding intensityvalues.

[0026] In one embodiment, substantially removing the correspondingintensity values can include modifying the intensity values of each oneof the wavelengths such that the sum the intensity values of each one ofthe wavelengths is equal to zero and the sum of the squares of theintensity values of each one of the wavelengths is equal to one.

[0027] In one embodiment, determining the endpoint based on thedifference between the normalized first spectrum data and the normalizedsecond spectrum data can include determining a change in the proportionsof normalized intensity for at least a portion of the plurality ofwavelengths in the first spectra and the second spectra.

[0028] In one embodiment, determining the change in the proportions ofnormalized intensity for at least a portion of the wavelengths in thefirst spectra and the second spectra can include converting thenormalized first spectrum data into a first vector and converting thenormalized second spectrum data into a second vector. A distance betweenthe first vector and the second vector can be calculated. The distancebetween the first vector and the second vector can be compared to athreshold distance and if the distance between the first and secondvectors is greater than or equal to a threshold distance, then a changein the proportions of normalized intensity for at least a portion of theplurality of wavelengths in the first spectra and the second spectra isidentified.

[0029] Another embodiment can include a plasma etch system that includesa broadband light source for illuminating a portion of a surface of awafer for multiple shots. An optical detector for receiving reflectedspectrum data corresponding to multiple spectrums of light reflectedfrom the illuminated portion of the surface of the wafer for each of theshots. Logic for normalizing a first reflected spectrum datacorresponding to a first shot is also included. Logic for normalizing asecond reflected spectrum data corresponding to a second shot and logicfor determining an endpoint based on a difference between the normalizedfirst spectrum data and the normalized second spectrum data are alsoincluded.

[0030] The logic for determining the endpoint based on the differencebetween the normalized first spectrum data and the normalized secondspectrum data can include logic for determining a change in theproportions of intensity for at least a portion of the wavelengths inthe first spectra and the second spectra. Determining the change in theproportions of intensity for at least a portion of the wavelengths inthe first spectra and the second spectra can include logic forconverting the normalized first spectrum data into a first vector, logicfor converting the normalized second spectrum data into a second vector,logic for calculating a distance between the first vector and the secondvector, logic for determining if the distance between the first andsecond vectors is greater than or equal to a threshold distance, andlogic for identifying a change in the proportions of intensity for atleast a portion of the plurality of wavelengths in the first spectra andthe second spectra, if the distance between the first and second vectorsis greater than or equal to the threshold distance.

[0031] Another embodiment is a system of detecting an endpoint. Thesystem includes a broad band light source for illuminating a portion ofa surface of a wafer for multiple shots. An optical detector forreceiving reflected spectrum data corresponding to multiple spectrums oflight reflected from the illuminated portion of the surface of the waferfor each of the shots is also included. Logic for normalizing a firstreflected spectrum data corresponding to a first shot and logic fornormalizing a second reflected spectrum data corresponding to a secondshot and logic for determining an endpoint based on a difference betweenthe normalized first spectrum data and the normalized second spectrumdata are also included.

[0032] The logic for determining the endpoint based on the differencebetween the normalized first spectrum data and the normalized secondspectrum data can include logic for determining a change in theproportions of intensity for at least a portion of the wavelengths inthe first spectra and the second spectra. Determining the change in theproportions of intensity for at least a portion of the plurality ofwavelengths in the first spectra and the second spectra can includelogic for converting the normalized first spectrum data into a firstvector, logic for converting the normalized second spectrum data into asecond vector, logic for calculating a distance between the first vectorand the second vector, logic for determining if the distance between thefirst and second vectors is greater than or equal to a thresholddistance, and logic for identifying a change in the proportions ofintensity for at least a portion of the wavelengths in the first spectraand the second spectra, if the distance between the first and secondvectors is greater than or equal to the threshold distance.

[0033] The first spectrum data can include an intensity levelcorresponding to each of multiple wavelengths in the corresponding firstspectra. The multiple wavelengths in the corresponding first spectra caninclude a range of about 300 nm to about 720 nm. The multiplewavelengths in the corresponding first spectra include a range of about200 to about 520 individual data points.

[0034] The logic for normalizing the first spectrum data includes logicfor substantially removing the corresponding intensity values. The logicfor substantially removing the corresponding intensity values includeslogic for modifying the intensity values of each one of the wavelengthssuch that the sum the intensity values of each one of the wavelengths isequal to zero the sum of the squares of the intensity values of each oneof the wavelengths is equal to one. The system of detecting an endpointcan also be included in a proximity processing head.

[0035] Other aspects and advantages of the invention will becomeapparent from the following detailed description, taken in conjunctionwith the accompanying drawings, illustrating by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention will be readily understood by the followingdetailed description in conjunction with the accompanying drawings, andlike reference numerals designate like structural elements.

[0037]FIGS. 1A and 1B show a cross sectional view of a dielectric layerundergoing a fabrication process that is common in constructingdamascene and dual damascene interconnect metallization lines.

[0038]FIG. 2A shows a CMP system in which a pad is designed to rotatearound rollers, in accordance with an embodiment of the presentinvention.

[0039]FIG. 2B is a endpoint detection system in accordance with oneembodiment of the present invention.

[0040]FIG. 3 is a diagram showing a portion of a wafer illuminated by abroad band light source during a CMP process, in accordance with oneembodiment of the present invention.

[0041]FIG. 4A is a flowchart diagram that illustrates the methodoperations performed in determining an endpoint for a CMP process inaccordance with one embodiment of the present invention.

[0042]FIG. 4B is a flowchart diagram of the method operations 450 incalculating a change in proportions for at least a portion of thewavelengths in the first and second spectra in accordance with oneembodiment of the present invention.

[0043]FIG. 5A illustrates one received reflected spectrum of data (i.e.,shot) in accordance with one embodiment of the present invention.

[0044]FIG. 5B illustrates one normalized reflected spectrum of data(i.e. a normalized shot) in accordance with one embodiment of thepresent invention.

[0045]FIG. 5C is a three dimensional graphical illustration of severalnon-normalized shots in accordance with one embodiment of the presentinvention.

[0046]FIGS. 6 and 7 are graphs of the data shown in FIG. 5C above, inaccordance with one embodiment of the present invention.

[0047]FIGS. 8 and 9 are two-dimensional graphs of the data shown in FIG.5C above that have been enhanced in accordance with one embodiment ofthe present invention.

[0048]FIG. 10 is a graphical representation of reflected data that has achange of reflecting coefficient by wavelength with time that has notbeen normalized relative to intensity, in accordance with one embodimentof the present invention.

[0049]FIG. 11 is a graphical representation of reflected data that hasan intensity normalized reflecting coefficient change in accordance withone embodiment of the present invention.

[0050]FIG. 12 is a flowchart diagram of method operations fordetermining an endpoint in accordance with one embodiment of the presentinvention.

[0051]FIG. 13 is a graph of the vector distance squared (VD) of amaterial removal process in accordance with one embodiment of thepresent invention.

[0052]FIG. 14 is a flowchart of the method operations of performing astress-free planarization etch process, in accordance with oneembodiment of the present invention.

[0053]FIG. 15A illustrates a proximity head performing an exemplarywafer processing operation in accordance with one embodiment of thepresent invention.

[0054]FIG. 15B shows a top view of a portion of a proximity head inaccordance with one embodiment of the present invention.

[0055]FIG. 16A illustrates an exemplary proximity head, in accordancewith one embodiment of the present invention.

[0056]FIG. 16B illustrates a sectional view of the proximity head andthe meniscus formed by the proximity head, in accordance with oneembodiment of the present invention.

[0057]FIG. 17 shows a wafer processing system in accordance with oneembodiment of the present invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0058] Several exemplary embodiments for optically determining anendpoint will now be described. It will be apparent to those skilled inthe art that the present invention may be practiced without some or allof the specific details set forth herein.

[0059] An important control aspect of the chemical mechanical polishing(CMP) system is determining when the process is at an end, i.e., when tostop the CMP process. Prior art systems described above, typicallypredict and endpoint based on various detected data points but cannotaccurately detect an exact endpoint as will be described in more detailbelow.

[0060] While the various embodiments of endpoint detection systems andmethods that are discussed herein are described in an exemplaryapplication of a CMP processes and CMP systems, it should be understoodthat the endpoint detection systems and methods can be applied in anyother type of system or method. By way of example, the endpointdetection methods and systems described herein can be used in astand-alone system that can be used in conjunction with any process orsystem. Further, the endpoint detection methods and systems describedherein can be used in a proximity head systems and methods such asdescribed in co-owned U.S. patent application Ser. No. 10/330,843 filedon Dec. 24, 2002 and entitled “Meniscus, Vacuum, IPA Vapor, DryingManifold,” which is a continuation-in-part of co-pending U.S. patentapplication Ser. No. 10/261,839 filed on Sep. 30, 2002 and entitled“Method and Apparatus for Drying Semiconductor Wafer Surfaces Using aPlurality of Inlets and Outlets Held in Close Proximity to the WaferSurfaces,” both of which are incorporated herein by reference in itsentirety. Additional embodiments and uses of the proximity head are alsodisclosed in U.S. patent application Ser. No. 10/330,897, filed on Dec.24, 2002, entitled “System for Substrate Processing with Meniscus,Vacuum, EPA vapor, Drying Manifold” and U.S. patent application Ser. No.10/404,692, filed on Mar. 31, 2003, entitled “Methods and Systems forProcessing a Substrate Using a Dynamic Liquid Meniscus.” Stilladditional embodiments of the proximity head are described in U.S.patent application Ser. No. 10/404,692, filed on Mar. 31, 2003, entitled“Methods and Systems for Processing a Substrate Using a Dynamic LiquidMeniscus” and U.S. patent application Ser. No. 10/603,427, filed on Jun.24, 2003, and entitled “Methods and Systems for Processing a Bevel Edgeof a Substrate Using a Dynamic Liquid Meniscus.” The aforementionedapplications being incorporated by reference in their entirety.

[0061] The endpoint detection methods and systems described herein canbe also used in a plasma-etch process such as described in U.S. patentapplication Ser. No. 10/390,520, filed on Mar. 14, 2003, and entitled“System, Method and Apparatus for Improved Local Dual-DamascenePlanarization” and U.S. patent application Ser. No. 10/390,117, filed onMar. 14, 2003, and entitled “System, Method and Apparatus for ImprovedGlobal Dual-Damascene Planarization.” The aforementioned applicationsbeing incorporated by reference in their entirety.

[0062]FIG. 2A shows a CMP system in which a pad 250 is designed torotate around rollers 251, in accordance with an embodiment of thepresent invention. A platen 254 is positioned under the pad 250 toprovide a surface onto which a wafer will be applied using a carrier252. Endpoint detection is performed using an optical detector 260 inwhich light is applied through the platen 254, through the pad 250 andonto the surface of the wafer 200 being polished, as shown FIG. 2B. Inorder to accomplish optical endpoint detection, a pad slot 250 a isformed into the pad 250. In some embodiments, the pad 250 may include anumber of pad slots 250 a strategically placed in different locations ofthe pad 250. Typically, the pad slots 250 a are designed small enough tominimize the impact on the polishing operation. In addition to the padslot 250 a, a platen slot 254 a is defined in the platen 254. The platenslot 254 a is designed to allow the broad band optical beam to be passedthrough the platen 254, through the pad 250, and onto the desiredsurface of the wafer 200 during polishing.

[0063] By using the optical detector 260, it is possible to ascertain alevel of removal of certain films from the wafer surface. This detectiontechnique is designed to measure the thickness of the film by inspectingthe interference patterns received by the optical detector 260.Additionally, the platen 254 is designed to strategically apply certaindegrees of back pressure to the pad 250 to enable precision removal ofthe layers from the wafer 200.

[0064]FIG. 3 is a diagram showing a portion of a wafer 300 illuminatedby a broad band light source during a CMP process, in accordance withone embodiment of the present invention. The wafer 300 includes asilicon substrate 302, an oxide layer 304 disposed over the substrate302, and a copper layer 306 formed over the oxide layer 304. The copperlayer 306 represents overburdened copper formed during a Damascene CMPprocess. Generally, the copper layer 306 is deposited over the oxidelayer 304, which is etched in an earlier step to form trenches forcopper interconnects. The overburden copper is then removed by polishingto expose the oxide layer 304, thus leaving only the conductive lineswithin the trenches. Dual Damascene occurs in a similar manner andallows the formation of metal plugs and interconnects at the same time.

[0065] During the polishing process, an optical endpoint detectionsystem uses the optical interference to determine when the copper 306has been removed. Initially, shown in view 301 a, the copper layer 306is relatively thick (e.g., about 10,000 Å) and thus opaque. At thispoint, the light 308 that illuminates the surface of the wafer 300 isreflected back with little or no interference. As the copper is polisheddown, the copper layer 306 becomes a thin metal (e.g., at about 300-400Å thick). This is known as the thin metal zone. At this point, shown inview 301 b, the copper layer 306 becomes transparent to at least somewavelengths of the light 312 and those wavelengths can pass through thecopper layer 306 to illuminate the layers beneath.

[0066] When some wavelengths of the light 312 begin illuminating thelayer 304, other wavelengths of the light 312 continue to reflect backfrom the surface of the thin metal zone copper layer 306. The intensityof the reflected wavelengths of light 318 that are reflected from theinterface between layer 304 and layer 302, below the copper layer 306,is different than the intensity of the same wavelengths of light 314reflected from the copper layer 306. However, only the intensities ofthe wavelengths that are reflecting from the interface between layer 304and layer 302 will change. The intensities of the remaining wavelengthsof light 314 that are reflected from the copper layer 306 will notchange.

[0067] One reason the intensities of the wavelengths of light 318 changeis due to the fact that each of the various layers 302-306 have acorresponding reflective index. The reflective index impacts theintensity of the light reflected from that layer.

[0068] As the copper is fully removed, as shown in view 301 c, thecopper layer 306 is no longer present to reflect or block the passage ofany of the wavelengths of the light 322. Therefore, all wavelengths ofthe light 322 can then illuminate the layer 304 that lies below thecopper layer 306. Substantially all wavelengths of the light 324reflected back from the layer 304 will have a change in intensity levelas compared to the intensity of the same wavelengths of light reflectedfrom the copper layer 306.

[0069] The optical detector 260 detects the reflected light 308, 314,318, 324. Therefore, in one embodiment of the present invention, anendpoint is determined when substantially all of the wavelengths of thereflected light experience a change in intensity.

[0070] Thus, when the copper layer 306 is thick, the intensities of thewavelengths of light 308 do not change. However, multiple otherinterference source such as slurry thicknesses, belt interference, andother sources can cause intensity “noise” that can cause the intensitiesof all the wavelengths of reflected light to change. Therefore, theendpoint must be differentiated from the various intensity noisesources. In one embodiment, the present invention can detect the actualend point and differentiate that endpoint from various intensity noisesources.

[0071]FIG. 4A is a flowchart diagram that illustrates the methodoperations performed in determining an endpoint for a CMP process inaccordance with one embodiment of the present invention. In operation402 a first portion of a surface of a wafer is illuminated with firstbeam of broad band light. In operation 404, a first reflected spectrumdata (i.e., a first shot) is received. The first shot corresponds to afirst set of spectra of light reflected from the first illuminatedportion of the surface of the wafer. In one embodiment, the first shotincludes an intensity level corresponding to each of several wavelengthsin the corresponding first spectra. In one embodiment, the firstreflected spectra are in the range of about 200 nm to about 720 nmwavelengths. The number of individual wavelengths that can be detectedis limited only by the ability of the optical detector 260. In oneembodiment, 512 individual wavelengths are detected, however, fewer or agreater number of individual wavelengths can also be detected.

[0072] In operation 406 a second portion of a surface of a wafer isilluminated with second beam of broad band light. In operation 408, asecond reflected spectrum data is received (i.e., a second shot). Thesecond shot corresponds to a second set of spectra of light reflectedfrom the second illuminated portion of the surface of the wafer.

[0073]FIG. 5A illustrates one received reflected spectrum of data (i.e.,shot) in accordance with one embodiment of the present invention, suchas the first shot received in operation 404 of FIG. 4A above.Approximately 512 individual wavelengths are shown across the x-axis.The intensity is shown on the y-axis.

[0074] Referring again to FIG. 4A, in operations 410 and 412,respectively, the first shot and the second shot are normalized.According to one embodiment, normalizing the first shot and the secondshot includes substantially removing the intensity aspect from theshots. In one embodiment, the intensity is substantially removed byadjusting the intensity of each of the detected wavelengths such that asum of the total intensities of all detected wavelengths is equal tozero and sum of squares of the total intensities of all detectedwavelengths is equal to one.

[0075]FIG. 5B illustrates one normalized reflected spectrum of data(i.e. a normalized shot) in accordance with one embodiment of thepresent invention, such as the normalized first shot as determined inoperation 410 of FIG. 4 above. Approximately 512 individual wavelengthsare shown across the x-axis. The intensity is shown on the y-axis. Thesum of the intensities is equal to zero and sum of squares of the totalintensities of all detected wavelengths is equal to one. The methodoperations of normalizing a shot will be described in more detail below.

[0076] Referring again to FIG. 4A, in operation 414, a differencebetween the normalized first shot and the normalized second shot isdetermined and is used to determine an endpoint of the CMP process. Inone embodiment, determining a difference between the normalized firstshot and the normalized second shot includes determining a change in theproportions of intensity for at least a portion of the wavelengths inthe first and second spectra.

[0077]FIG. 4B is a flowchart diagram of the method operations 450 incalculating a change in proportions for at least a portion of thewavelengths in the first and second spectra in accordance with oneembodiment of the present invention. In operation 452, the normalizedfirst spectrum data is converted to a first vector. In operation 454,the normalized second spectrum data is converted to a second vector. Inoperation 456, a distance between the first and second vectors iscalculated. The distance between the first and second vectors iscompared to a threshold distance to determine if the distance betweenthe first and second vectors is greater than or equal to a thresholddistance, in operation 458. If the distance between the first and secondvectors is greater than or equal to the threshold distance, then achange in proportions of the intensity is identified for at least aportion of the wavelengths in the first and second spectra, in operation460 and the method operations end.

[0078]FIG. 5C is a three dimensional graphical illustration of severalnon-normalized shots in accordance with one embodiment of the presentinvention. The wavelengths in nm ranging from approximately 200 nm atthe origin end of the z-axis to approximately 800 nm. Intensity is shownon the y-axis. The x-axis shows the number of shots, approximately 13shots (shots 3-15) are shown. The number of shots shown can correspondto CMP processing time (i.e., polishing time). In one embodiment, thesampling rate is a function of the polishing belt speed and the amountof the end point detection windows in the belt. A line in the x-axis isdrawn to connect the intensity of a given wavelength in a first shot tothe intensity of the same wavelength in a subsequent shot. For example,pointer 551 identifies intensity level of approximately 310 nm in shot 3(shots 0-2 are not shown). Pointer 552 identifies the correspondingintensity level of the same 310 nm wavelength in shot 4. The intensitiesof the various detected wavelengths vary from shot to shot but thevariations are substantially proportionate in that the intensities ofall wavelengths shift upward or downward at the same time. Thisindicates noise in the intensity dimension but does not indicate achange in the actual surface material reflecting the shot.

[0079] On the 13^(th) shot (pointer 555) begins a marked downward trendin the intensities of all wavelengths, for subsequent shots 14 and 15,is shown. The downward trend indicated by pointer 555 identifies achange in the material reflecting the shot.

[0080]FIGS. 6 and 7 are graphs of the data shown in FIG. 5C above, inaccordance with one embodiment of the present invention. In FIG. 6, thereflected data includes unwanted information such as absolute intensitychanges that result in wide variations in the intensity of the reflectedlight for each of the shots shown.

[0081] Conversely, FIG. 7 illustrates the same reflected data that hasbeen normalized to a relative intensity. Normalizing results in a narrowvariation in the intensity of the reflected light for each of the shotsshown.

[0082] The resolution of the reflected data can be increased byanalyzing the reflecting coefficient change rather than the absoluteintensity value. The reflecting coefficient change can be generated byFormula 2 as follows:

[0083] A change in the reflecting coefficient can indicate an endpoint(i.e., when the desired layer is fully removed).

[0084]FIGS. 8 and 9 are two-dimensional graphs of the data shown in FIG.5C above that have been enhanced in accordance with one embodiment ofthe present invention. In FIG. 8, the absolute value of the reflectingcoefficient by wavelength and time is shown. In FIG. 9, the change ofreflecting coefficient by wavelength with time is shown. This stepsprovides a characteristic signature of the film (material reflecting thelight) is dependent on an interference effect. The characteristics oftransparent film, i.e., where two surfaces meet, will reflect the light.For copper processes, the change in reflected data includes changingfrom opaque in visible spectra copper to a transparent film layer belowthe copper layer. After the reflected data is obtained in qualitativefashion described above, the data can be processed to build an endpointdetection based on this change.

[0085]FIG. 10 is a graphical representation of reflected data that has achange of reflecting coefficient by wavelength with time that has notbeen normalized relative to intensity, in accordance with one embodimentof the present invention. FIG. 11 is a graphical representation ofreflected data that has an intensity normalized reflecting coefficientchange in accordance with one embodiment of the present invention. FIG.11 demonstrates that measured value changes from straight line 1102,1104 with some high frequency oscillations into well-defined sinusoidalinterference related oscillations 1106, 1108, 1110,1112 and those lineswith transitional states 1114, 1116.

[0086] A second characteristic of transparent films and a function ofthickness and refractory index (not shown) can also influence thereflected data. For example, sinusoidal function of differentfrequencies relates to transition from one film to another.

[0087]FIG. 12 is a flowchart diagram of method operations 1200 fordetermining an endpoint in accordance with one embodiment of the presentinvention. In operation 1210, a reflecting coefficient for wafer for afirst shot is calculated according to Formula 3 as follows:

R _(i)(λ_(j))=I _(wi)(λ_(j))I _(Li)(λ_(j)), j=1, . . . , 512  Formula 3:

[0088] In operation 1215, the reflecting coefficient is normalized andpresented in relative intensity units according to Formula 4 as follows:Formula  4:${{R_{i}^{\backprime}\left( \lambda_{j} \right)} = {{R_{i}\left( \lambda_{j} \right)}/\left. \sqrt{}S \right.}},{{{where}\quad S} = {\sum\limits_{j = 1}^{512}{R_{i}^{2}\left( \lambda_{j} \right)}}},{j = 1},\ldots \quad,512$

[0089] In operation 1220, a change in the normalized reflectingcoefficient (i.e., the change in material) is calculated according toFormula 5 as described above follows: $\begin{matrix}{\text{Formula~~~5:}{{{THE}\quad {Change}} = \left\{ {\overset{\rightarrow}{R_{i}^{\backprime}} - \overset{\rightarrow}{R_{k}^{\backprime}}} \right\}}} & \quad\end{matrix}$

[0090] In operation 1225, the vector distance square (VD) between thecurrent R′_(i) and a pre-selected recipe reference value R′_(k) iscalculated according to Formula 6 as follows: $\begin{matrix}{\text{Formula~~~6:}{{{VD} = {\underset{J = 1}{\sum\limits^{512}}\quad \left\{ {{\overset{\rightarrow}{R_{i}^{\backprime}}\left( \lambda_{j} \right)} - {\overset{\rightarrow}{R_{k}^{\backprime}}\left( \lambda_{j} \right)}} \right\}^{2}}},{j = 1},\ldots \quad,512}} & \quad\end{matrix}$

[0091] In operation 1230, the calculated vector distance is compared toa threshold vector distance. The threshold VD can be a known change invector distance that was determined from previous experience withremoving the layer to be removed to reveal an underlying layer, in oneembodiment. Alternatively, the threshold VD can be a pre-selected numberindicating a direction in the change (e.g., an upward or a downwardtrend in the normalized reflecting coefficient. If the calculated VD isnot greater than the threshold VD, then the I_(wi)(λ) and the I_(Li) (λ)are input to operation 1210 as described above and the method operations1210-1230 repeat. If, however, in operation 1230, the calculated VD isgreater than or equal to the threshold VD, then the end point has beendetermined and the CMP process can be stopped immediately.

[0092]FIG. 13 is a graph of the vector distance squared (VD) of amaterial removal process in accordance with one embodiment of thepresent invention. The y-axis is the VD. The x-axis is time or moreprecisely shot number. From the origin to approximately the 12^(th)shot, the graph shows the VD remains approximately constant value. TheVD between the 12^(th) shot and the 13^(th) shot are much greater asshown by the graph. The change in the VD illustrated at the 12^(th) shotindicates the endpoint has been detected.

[0093] While various aspects and embodiments of the invention have beendescribed above relating to determining an endpoint when removing acopper layer, it should be understood that the methods and systemsdescribed herein can be similarly applied to the removal process of anyother material. The methods and systems described herein can besimilarly applied to the removal of other opaque or non-opaque materialsthat are overlaying a different opaque or non-opaque material. By way ofexample, methods and systems described herein can be used to determinean endpoint of the removal process for removing an oxide layer(non-opaque layer) over a copper layer (opaque layer). Similarly, anendpoint for removing an oxide layer (non-opaque layer) over anothernon-opaque material layer.

[0094] While various aspects and embodiments of the invention have beendescribed above relating to determining an endpoint using 512 separatedata points (e.g., wavelengths) along the spectrum of the reflectedbroad band light (e.g., Formula 6 wherein j=1-512). However, the presentinvention is not limited to only 512 separate data points and any numberof data points can be used. The number of data points used is analogousto the granularity of the data received. For finer resolution of thedata, a greater number of individual data points must be collected andused. However, the greater number of individual data points that arecollected also increases the computational load. 512 individual datapoints are used to illustrate one level of granularity of the process.Fewer individual data points such as about 200 or less can also used.Alternatively, additional wavelengths can also be used such as more thanabout 520 data points.

[0095] As discussed herein two different scales are used for the samebroad bandwidth light. A first scale is the wavelengths included in thespectrum of the broad band light. In one embodiment the spectrum of thebroad band light is from about 300 to about 720 nm. However, thespectrum of broadband light that is used can be expanded to includeshorter and/or longer wavelengths of light. In one embodiment thespectrum of broadband light is selected to correspond to the materialsbeing processed in the CMP process. In one embodiment, a wider spectrumcan be used for a wider variety of materials.

[0096] A second scale used to describe the detection of the broadbandwidth light is the number of data points that are distributed acrossthe spectrum of the broadband light. In one embodiment, if the number ofdata points is 512 and the broadband spectrum is from about 300 to about720 nm, then the first data point corresponds to a wavelength ofapproximately 298.6 nm and the 512 data point corresponds to wavelengthapproximately 719.3 nm. The number and distribution of the data pointsacross the broadband spectrum is determined by the particularmanufacturer of the optical detector. Typically, the data points areevenly distributed across the spectrum. The data points can also bereferred to as a pixel.

[0097] The above-described endpoint detection process can also be usedin a stress-free etch process such as described in U.S. patentapplication Ser. No. 10/390,520, filed on Mar. 14, 2003, and entitled“System, Method and Apparatus for Improved Local Dual-DamascenePlanarization” and U.S. patent application Ser. No. 10/390,117, filed onMar. 14, 2003, and entitled “System, Method and Apparatus for ImprovedGlobal Dual-Damascene Planarization.” The aforementioned applicationsbeing incorporated by reference in their entirety.

[0098]FIG. 14 is a flowchart 1400 of the method operations of performinga stress-free planarization etch process, in accordance with oneembodiment of the present invention. In operation 1405, an additionallayer is added on top of a conductive overburden portion. In operation1410, the first etch process is applied to remove the majority of theadditional layer and the conductive overburden portion. In operation1415, the second etch process is applied to remove the remainingoverburden portion until an endpoint is achieved.

[0099] The endpoint detection methods and systems described herein canbe used in a proximity head systems and methods such as described inco-owned U.S. patent application Ser. No. 10/330,843 filed on Dec. 24,2002 and entitled “Meniscus, Vacuum, IPA Vapor, Drying Manifold,” whichis a continuation-in-part of co-pending U.S. patent application Ser. No.10/261,839 filed on Sep. 30, 2002 and entitled “Method and Apparatus forDrying Semiconductor Wafer Surfaces Using a Plurality of Inlets andOutlets Held in Close Proximity to the Wafer Surfaces,” both of whichare incorporated herein by reference in its entirety. Additionalembodiments and uses of the proximity head are also disclosed in U.S.patent application Ser. No. 10/330,897, filed on Dec. 24, 2002, entitled“System for Substrate Processing with Meniscus, Vacuum, EPA vapor,Drying Manifold” and U.S. patent application Ser. No. 10/404,692, filedon Mar. 31, 2003, entitled “Methods and Systems for Processing aSubstrate Using a Dynamic Liquid Meniscus.” Still additional embodimentsof the proximity head are described in U.S. patent application Ser. No.10/404,692, filed on Mar. 31, 2003, entitled “Methods and Systems forProcessing a Substrate Using a Dynamic Liquid Meniscus,” U.S. patentapplication Ser. No. 10/603,427, filed on Jun. 24, 2003, and entitled“Methods and Systems for Processing a Bevel Edge of a Substrate Using aDynamic Liquid Meniscus,” and U.S. patent application Ser. No.10/606,022, filed on Jun. 24, 2003, and entitled “System and Method forIntegrating In-Situ Metrology within a Wafer Process.” Theaforementioned applications being incorporated by reference in theirentirety.

[0100]FIG. 15A illustrates a proximity head 1520 performing an exemplarywafer processing operation in accordance with one embodiment of thepresent invention. The proximity head 1520, in one embodiment, moveswhile in close proximity to the top surface 1530 a of the wafer 1530 toconduct a cleaning, drying, etching or other processing operation. Itshould be appreciated that the proximity head 1530 may also be utilizedto process (e.g., clean, dry, etc.) the bottom surface 1530 b of thewafer 1530. In one embodiment, the wafer 1530 is rotating so theproximity head 1520 may be moved in a linear fashion along the headmotion while fluid is removed from the top surface 1530 a. By applyingthe IPA 1510 through the source inlet 1502, the vacuum 1512 throughsource outlet 1504, and the deionized water 1514 through the sourceinlet 1506, the meniscus 1516 can be generated.

[0101]FIG. 15B shows a top view of a portion of a proximity head 1520 inaccordance with one embodiment of the present invention. In the top viewof one embodiment, from left to right are a set of the source inlet1502, a set of the source outlet 1504, a set of the source inlet 1506, aset of the source outlet 1504, and a set of the source inlet 1502.Therefore, as N₂/IPA and DIW are inputted into the region between theproximity head 1520 and the wafer 1530, the vacuum removes the N₂/IPAand the DIW along with any fluid film that may reside on the wafer 1530.The source inlets 1502, the source inlets 1506, and the source outlets1504 described herein may also be any suitable type of geometry such asfor example, circular opening, square opening, etc. In one embodiment,the source inlets 1502 and 1506 and the source outlets 1504 havecircular openings.

[0102]FIG. 16A illustrates an exemplary proximity head 1600, inaccordance with one embodiment of the present invention. FIG. 16Billustrates a sectional view of the proximity head 1600 and the meniscus1650 formed by the proximity head 1600, in accordance with oneembodiment of the present invention. The proximity head 1600 includes aring of multiple process chemistry inlets 1604, two rings of multipleEPA inlets 1602 and 1608 and a ring of multiple vacuum outlets 1606. Thevarious inlets 1602, 1604, 1606 and outlets 1608 are arranged around asensor 1620. The sensor 1620 is a metrology sensor that can evaluate theprogress of the fabrication process being applied by the processing head1600. The sensor can be an optical end-point detection sensor so as toenable the above-described endpoint detection systems and methods to beused.

[0103] The meniscus 1650 can include a “dry” central region 1652 wherethe liquid meniscus is removed so that the sensor 1620 has nointervening processing chemistry from the meniscus 1650 between thesensor and the surface of the wafer 1530. Rotating the wafer 1530 andscanning the proximity head 1600, and therefore the sensor 1620, acrossthe wafer 1530 can provide an in-situ scan of the entire surface of thewafer, as the proximity head processes the wafer. The sensor 1620 canalso provide real time feedback of the etch process. Providing the realtime feedback to a control system that controls the etch process willprovide a closed control loop of the etch process. The closed loopcontrol of the etch process can allow the control system tointeractively adjust the etch process in real time. Any of the multipleetch process variables can be adjusted including head position,concentrations, resident time, flow rates, pressures, chemistry andother process variables. In this manner more precise process control isprovided. A more precise process control allows ever more concentratedetch chemistries to be used, which in turn reduces the process time ofthe wafer to a minimum.

[0104] The in-situ, real time control of the process can also enable avariable process to be applied to the surface of the wafer such as tocorrect for a non-uniformity during the processing of the wafer. By wayof example, if in an etch process, the sensor can detect a thinner filmin a first region of the wafer 1530 and a thicker film in a secondregion. The etch process recipe can be dynamically adjusted (e.g., etchchemistry concentration, residence time, etc.) for the detected filmthickness as the proximity head 1600 scans across the wafer 1530. As aresult, the non-uniform film thickness can be dynamically correctedin-situ as the etch process is applied to the wafer 1530 therebysubstantially eliminating the need for reprocessing the wafer to correctfor non-uniformities.

[0105] In an alternative embodiment, the dry region 1652 is notrequired. By way of example, if the sensor 1620 can measure filmthickness through a layer of liquid (e.g., the meniscus 1650) such asthe process chemistry being applied to the surface of the wafer 1530.

[0106]FIG. 17 shows a wafer processing system 1700 in accordance withone embodiment of the present invention. The wafer processing system1700 supports a wafer 1530 between multiple edge rollers 1712A-1712C. Amovable arm 1714A supports and moves a proximity head 1520 over thesurface of the wafer 1530. An in-situ sensor 1702 can be mounted on thearm 1714A, external of the proximity head 1520 (not shown) or can bemounted on a separate movable arm 1704 that can move independent of themovable arm 1714A that supports the proximity head 1520. As a result,the sensor 1702 can scan and measure corresponding locations near theprocess being applied to the wafer 1530 by the proximity head 1520.Alternatively, the sensor 1702 can measure corresponding locations nearthe process being applied to the wafer 1530 by the proximity head 1520and can independently scan locations on the surface of the wafersubstantially simultaneously as the proximity head applies a process tothe wafer.

[0107] With the above embodiments in mind, it should be understood thatthe invention may employ various computer-implemented operationsinvolving data stored in computer systems. These operations are thoserequiring physical manipulation of physical quantities. Usually, thoughnot necessarily, these quantities take the form of electrical ormagnetic signals capable of being stored, transferred, combined,compared, and otherwise manipulated. Further, the manipulationsperformed are often referred to in terms, such as producing,identifying, determining, or comparing.

[0108] Any of the operations described herein that form part of theinvention are useful machine operations. The invention also relates to adevice or an apparatus for performing these operations. The apparatusmay be specially constructed for the required purposes, or it may be ageneral-purpose computer selectively activated or configured by acomputer program stored in the computer. In particular, variousgeneral-purpose machines may be used with computer programs written inaccordance with the teachings herein, or it may be more convenient toconstruct a more specialized apparatus to perform the requiredoperations.

[0109] The invention can also be embodied as computer readable code on acomputer readable medium. The computer readable medium is any datastorage device that can store data that can be thereafter be read by acomputer system. Examples of the computer readable medium include harddrives, network attached storage (NAS), read-only memory, random-accessmemory, CD-ROMs, CD-Rs, CD-RWs, magnetic tapes, and other optical andnon-optical data storage devices. The computer readable medium can alsobe distributed over a network coupled computer systems so that thecomputer readable code is stored and executed in a distributed fashion.

[0110] It will be further appreciated that the instructions representedby the operations in FIGS. 4A, 4B and 12 are not required to beperformed in the order illustrated, and that all the processingrepresented by the operations may not be necessary to practice theinvention. Further, the processes described in FIGS. 4A, 4B and 12 canalso be implemented in software stored in any one of or combinations ofcomputer readable medium.

[0111] Although the foregoing invention has been described in somedetail for purposes of clarity of understanding, it will be apparentthat certain changes and modifications may be practiced within the scopeof the appended claims. Accordingly, the present embodiments are to beconsidered as illustrative and not restrictive, and the invention is notto be limited to the details given herein, but may be modified withinthe scope and equivalents of the appended claims.

What is claimed is:
 1. A method for detecting an endpoint, comprising:illuminating a first portion of a surface of a wafer with first beam ofbroad band light; receiving a first reflected spectrum datacorresponding to a first plurality of spectra of light reflected fromthe first illuminated portion of the surface of the wafer; illuminatinga second portion of the surface of the wafer with second beam of broadband light; receiving a second reflected spectrum data corresponding toa second plurality of spectra of light reflected from the secondilluminated portion of the surface of the wafer; normalizing the firstreflected spectrum data; normalizing the second reflected spectrum data;and determining an endpoint based on a difference between the normalizedfirst spectrum data and the normalized second spectrum data.
 2. Themethod of claim 1, wherein the first spectrum data includes an intensitylevel corresponding to each of a plurality of wavelengths in thecorresponding first spectra.
 3. The method of claim 2, wherein theplurality of wavelengths in the corresponding first spectra includes arange of about 300 nm to about 720 nm.
 4. The method of claim 3, whereinthe plurality of wavelengths in the corresponding first spectra includesa range of about 200 to about 520 individual data points.
 5. The methodof claim 1, wherein normalizing the first spectrum data includessubstantially removing the corresponding intensity values.
 6. The methodof claim 5, wherein, substantially removing the corresponding intensityvalues includes modifying the intensity values of each one of theplurality of wavelengths such that the sum the intensity values of eachone of the plurality of wavelengths is equal to zero and the sum of thesquare of the intensity values of each one of the plurality ofwavelengths is equal to one.
 7. The method of claim 1, whereindetermining the endpoint based on the difference between the normalizedfirst spectrum data and the normalized second spectrum data includesdetermining a change in the proportions of intensity for at least aportion of the plurality of wavelengths in the first spectra and thesecond spectra.
 8. The method of claim 7, wherein, determining thechange in the proportions of intensity for at least a portion of theplurality of wavelengths in the first spectra and the second spectraincludes: converting the normalized first spectrum data into a firstvector; converting the normalized second spectrum data into a secondvector; calculating a distance between the first vector and the secondvector; determining if the distance between the first and second vectorsis greater than or equal to a threshold distance; and identifying achange in the proportions of intensity for at least a portion of theplurality of wavelengths in the first spectra and the second spectra, ifthe distance between the first and second vectors is greater than orequal to the threshold distance.
 9. A plasma etch system comprising: abroad band light source for illuminating a portion of a surface of awafer for a plurality of shots; an optical detector for receivingreflected spectrum data corresponding to a plurality of spectrums oflight reflected from the illuminated portion of the surface of the waferfor each of the plurality of shots; logic for normalizing a firstreflected spectrum data corresponding to a first shot; logic fornormalizing a second reflected spectrum data corresponding to a secondshot; and logic for determining an endpoint based on a differencebetween the normalized first spectrum data and the normalized secondspectrum data.
 10. The system of claim 9, wherein the logic fordetermining the endpoint based on the difference between the normalizedfirst spectrum data and the normalized second spectrum data includeslogic for determining a change in the proportions of intensity for atleast a portion of the plurality of wavelengths in the first spectra andthe second spectra.
 11. The system of claim 10, wherein, determining thechange in the proportions of intensity for at least a portion of theplurality of wavelengths in the first spectra and the second spectraincludes: logic for converting the normalized first spectrum data into afirst vector; logic for converting the normalized second spectrum datainto a second vector; logic for calculating a distance between the firstvector and the second vector; logic for determining if the distancebetween the first and second vectors is greater than or equal to athreshold distance; and logic for identifying a change in theproportions of intensity for at least a portion of the plurality ofwavelengths in the first spectra and the second spectra, if the distancebetween the first and second vectors is greater than or equal to thethreshold distance.
 12. A system of detecting an endpoint comprising: abroad band light source for illuminating a portion of a surface of awafer for a plurality of shots; an optical detector for receivingreflected spectrum data corresponding to a plurality of spectrums oflight reflected from the illuminated portion of the surface of the waferfor each of the plurality of shots; logic for normalizing a firstreflected spectrum data corresponding to a first shot; logic fornormalizing a second reflected spectrum data corresponding to a secondshot; and logic for determining an endpoint based on a differencebetween the normalized first spectrum data and the normalized secondspectrum data.
 13. The system of claim 12, wherein the logic fordetermining the endpoint based on the difference between the normalizedfirst spectrum data and the normalized second spectrum data includeslogic for determining a change in the proportions of intensity for atleast a portion of the plurality of wavelengths in the first spectra andthe second spectra.
 14. The system of claim 13, wherein, determining thechange in the proportions of intensity for at least a portion of theplurality of wavelengths in the first spectra and the second spectraincludes: logic for converting the normalized first spectrum data into afirst vector; logic for converting the normalized second spectrum datainto a second vector; logic for calculating a distance between the firstvector and the second vector; logic for determining if the distancebetween the first and second vectors is greater than or equal to athreshold distance; and logic for identifying a change in theproportions of intensity for at least a portion of the plurality ofwavelengths in the first spectra and the second spectra, if the distancebetween the first and second vectors is greater than or equal to thethreshold distance.
 15. The system of claim 12, wherein the firstspectrum data includes an intensity level corresponding to each of aplurality of wavelengths in the corresponding first spectra.
 16. Thesystem of claim 15, wherein the plurality of wavelengths in thecorresponding first spectra includes a range of about 300 nm to about720 nm.
 17. The system of claim 16, wherein the plurality of wavelengthsin the corresponding first spectra includes a range of about 200 toabout 520 individual data points.
 18. The system of claim 12, whereinthe logic for normalizing the first spectrum data includes logic forsubstantially removing the corresponding intensity values.
 19. Thesystem of claim 18, wherein, the logic for substantially removing thecorresponding intensity values includes logic for modifying theintensity values of each one of the plurality of wavelengths such thatthe sum the intensity values of each one of the plurality of wavelengthsis equal to zero the sum of the squares of the intensity values of eachone of the plurality of wavelengths is equal to one.
 20. The system ofclaim 12, wherein the system of detecting an endpoint is incorporated ina proximity processing head.